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><A
NAME="SERVER-SHUTDOWN"
>17.5. Shutting Down the Server</A
></H1
><P
>   There are several ways to shut down the database server. You control
   the type of shutdown by sending different signals to the master
   <TT
CLASS="COMMAND"
>postgres</TT
> process.

   <P
></P
></P><DIV
CLASS="VARIABLELIST"
><DL
><DT
><SPAN
CLASS="SYSTEMITEM"
>SIGTERM</SPAN
></DT
><DD
><P
>       This is the <I
CLASS="FIRSTTERM"
>Smart Shutdown</I
> mode.
       After receiving <SPAN
CLASS="SYSTEMITEM"
>SIGTERM</SPAN
>, the server
       disallows new connections, but lets existing sessions end their
       work normally. It shuts down only after all of the sessions terminate.
       If the server is in online backup mode, it additionally waits
       until online backup mode is no longer active.  While backup mode is
       active, new connections will still be allowed, but only to superusers
       (this exception allows a superuser to connect to terminate
       online backup mode).  If the server is in recovery when a smart
       shutdown is requested, recovery and streaming replication will be
       stopped only after all regular sessions have terminated.
      </P
></DD
><DT
><SPAN
CLASS="SYSTEMITEM"
>SIGINT</SPAN
></DT
><DD
><P
>       This is the <I
CLASS="FIRSTTERM"
>Fast Shutdown</I
> mode.
       The server disallows new connections and sends all existing
       server processes <SPAN
CLASS="SYSTEMITEM"
>SIGTERM</SPAN
>, which will cause them
       to abort their current transactions and exit promptly. It then
       waits for all server processes to exit and finally shuts down.
       If the server is in online backup mode, backup mode will be
       terminated, rendering the backup useless.
      </P
></DD
><DT
><SPAN
CLASS="SYSTEMITEM"
>SIGQUIT</SPAN
></DT
><DD
><P
>      This is the <I
CLASS="FIRSTTERM"
>Immediate Shutdown</I
> mode.
      The master <TT
CLASS="COMMAND"
>postgres</TT
> process will send a
      <SPAN
CLASS="SYSTEMITEM"
>SIGQUIT</SPAN
> to all child processes and exit
      immediately, without properly shutting itself down. The child processes
      likewise exit immediately upon receiving
      <SPAN
CLASS="SYSTEMITEM"
>SIGQUIT</SPAN
>. This will lead to recovery (by
      replaying the WAL log) upon next start-up. This is recommended
      only in emergencies.
      </P
></DD
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><P>
  </P
><P
>   The <A
HREF="app-pg-ctl.html"
><SPAN
CLASS="APPLICATION"
>pg_ctl</SPAN
></A
> program provides a convenient
   interface for sending these signals to shut down the server.
   Alternatively, you can send the signal directly using <TT
CLASS="COMMAND"
>kill</TT
>
   on non-Windows systems.
   The <ACRONYM
CLASS="ACRONYM"
>PID</ACRONYM
> of the <TT
CLASS="COMMAND"
>postgres</TT
> process can be
   found using the <TT
CLASS="COMMAND"
>ps</TT
> program, or from the file
   <TT
CLASS="FILENAME"
>postmaster.pid</TT
> in the data directory. For
   example, to do a fast shutdown:
</P><PRE
CLASS="SCREEN"
>$ <KBD
CLASS="USERINPUT"
>kill -INT `head -1 /usr/local/pgsql/data/postmaster.pid`</KBD
></PRE
><P>
  </P
><DIV
CLASS="IMPORTANT"
><BLOCKQUOTE
CLASS="IMPORTANT"
><P
><B
>Important: </B
>    It is best not to use <SPAN
CLASS="SYSTEMITEM"
>SIGKILL</SPAN
> to shut down
    the server.  Doing so will prevent the server from releasing
    shared memory and semaphores, which might then have to be done
    manually before a new server can be started.  Furthermore,
    <SPAN
CLASS="SYSTEMITEM"
>SIGKILL</SPAN
> kills the <TT
CLASS="COMMAND"
>postgres</TT
>
    process without letting it relay the signal to its subprocesses,
    so it will be necessary to kill the individual subprocesses by hand as
    well.
   </P
></BLOCKQUOTE
></DIV
><P
>   To terminate an individual session while allowing other sessions to
   continue, use <CODE
CLASS="FUNCTION"
>pg_terminate_backend()</CODE
> (see <A
HREF="functions-admin.html#FUNCTIONS-ADMIN-SIGNAL-TABLE"
>Table 9-55</A
>) or send a
   <SPAN
CLASS="SYSTEMITEM"
>SIGTERM</SPAN
> signal to the child process associated with
   the session.
  </P
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